Hydrocarbon conversion process



y 1, 1959 F. H. BLANDING 2,895,901

HYDROCARBON CONVERSION PROCESS Filed 001:. 5. 1953 /N VE N TOR c west a filamling ATTORNEY United States Patent assssini HYDROCARBON CONVERSION PROCESS Forrest H. Blending, Cranford, N.J., assignor to Esso Research and Engineering Company, a corporation of Delaware Application October 5, 1953, Serial No. 384,147

8 Claims. (Cl. 20873) This invention relates to the conversion of hydrocarbons to lower boiling components and more particularly relates to a process for conversion of hydrocarbons wherein the conversion to coke is minimized. Still more particularly the invention is concerned with a process which comprises a combination of catalytic and thermal cracking steps whereby a high ratio of gasoline to coke is effected.

Catalytic cracking of hydrocarbons is well known in the petroleum industry. This particular process has made it possible to produce gasoline from petroleum fractions, such as gas oils, which have a boiling range substantially above the gasoline boiling range. Because of this process it has been possible to substantially increase the proportion of gasoline obtained from crude oil. In addition the octane number of the gasoline produced by catalytic cracking is substantially higher than the octane number of the gasoline fraction of crude oil.

In the conventional catalytic cracking process, a hydrocarbon gas oil is contacted with a bed of catalytic material in a reactor to thereby convert the gas oil to lower boiling components. For this purpose a number of types of catalyst beds have been employed such as fixed beds, moving beds and fluidized beds, all of which are well known in the petroleum industry. During the contacting of the gas oil with the catalyst, in any of the aforementioned types of catalyst beds, a carbonaceous or cokelike deposit is laid down on the catalyst This carbonaceous deposit reduces the eifectiveness of the catalyst to convert the gas oil to lower boiling components and it is therefore necessary to remove this coke-like deposit from the catalyst, or in other words, to regenerate the catalyst so that the catalyst may be used for further catalytic cracking. This is accomplished by separating the spent catalyst from the hydrocarbons and burning off the coke-like deposit with an oxygen containing gas. Although'the catalyst prior to regeneration is normally called spent catalyst, its catalytic activity actually is only partially spent. In general, though, a major portion of its catalytic activity has been lost.

In the case of catalytic cracking processes employing the catalyst in the form of a fixed bed, the introduction of gas oil to the catalyst bed is discontinued when the catalyst becomes fouled with coke and the bed is then regenerated by introducing an oxygen-containing gas to the bed in order to burn off the carbonaceous or cokelike deposit on the spent catalyst. After regeneration, the catalyst bed can be utilized for further catalytic cracking. In the case of catalytic cracking processes employing catalyst in the form of a moving bed or a fluidized bed, the spent catalyst is withdrawn continuously from the reactor without interrupting the cracking process. An oxygen-containing gas is then combined with the spent catalyst and the mixture is introduced into a vessel called a regenerator in which the carbonaceous deposit on the spent catalyst is burned off. After regeneration the catalyst is returned to the reactor and again employed to catalytically crack more gas oil.

By changing reaction conditions, such as temperature, space velocity, residence time, etc., the conversion of gas oil to gasoline may be increased in a catalytic cracking process. However, in general, as the conversion of gas oil to gasoline is increased, the amount of coke formed and laid down on the catalyst also increases. Although it is desirable to maximize the amount of gas oil converted to gasoline, the extent of this conversion is thus limited by the amount of carbonaceous or coke-like deposits laid down on the catalyst and the facilities pro vided for burning off these carbonaceous deposits. Therefore, there is normally an economic balance between the conversion of gas oil to gasoline and the investment required for regeneration facilities. As regeneration facilities represent a substantial portion of the investment for a catalytic cracking system, the conversion of gas oil to gasoline in a given catalytic cracking system is therefore normally limited to the capacity of the regeneration facilities which were originally economically justified. Certain gas oils such as those which contain a large proportion of aromatics or are high in nitrogen will produce a substantially higher ratio of coke to gasoline than will parafiinic or naphthenic gas oils. Because of the high coke forming tendencies of these gas oils, it is normally necessary to reduce the conversion of gas oil to gasoline since the regeneration facilities limit the catalytic cracking system. Heretofore there was no way in which a relatively high conversion to gasoline could be obtained from such gas oils without building abnormally high capacity regeneration facilities.

An object of the present invention is to effect a high conversion of gas oil to gasoline while at the same time to minimize the amount of coke formed on the catalyst.

Another object of the present invention is to reduce the investment in regeneration facilities required for catalytic cracking systems.

A further object is to produce stable products from a catalytic cracking process.

Still further objects Will be apparent from a reading of this specification.

Briefly, the present invention comprises contacting a hydrocarbon gas oil substantially all of which boils above about 430 F. with a cracking catalyst at a temperature of about 850-l050 F. and preferably at a temperature of about 900-1000 P. so that between about 30-50% by volume of the hydrocarbon gas oil is converted to coke, gasoline and other components boiling below about 430 F., and so that not more than about 5% by weight of the hydrocarbon gas oil is converted to coke. The resultant vaporous hydrocarbon products are separated from the partially spent catalyst and are then maintained or soaked at a temperature between about 850-1050 F. and preferably at a temperature of about 900l000 F. for about 0.5-5 minutes so that about an additional 5-20% by volume of the hydrocarbons are converted to gasoline and other components boiling below about 430 F. During this soaking step of the present invention, substantially no coke is formed. However, because a certain amount of diolefins is produced during this soaking step, the resultant hydrocarbons are then contacted in an aftertreating step with additional catalyst, which is preferably the partially spent catalyst from the initial catalytic cracking step, so as to convert most of the diolefins to saturated hydrocarbon products to thereby improve the stability of the final products from the present invention. A minor amount of coke is formed and also a minor amount of additional conversion is effected in this catalytic aftertreating step. The process of the present invention thereby provides a high ratio of stable gasoline to coke and also, as a result, investment in regeneration facilities is minimized.

The initial contacting of the hydrocarbon gas oil with catalyst results in the major portion of the conversion of the hydrocarbon gas oil to high quality gasoline. The soaking step, or predominantly thermal cracking step, provides additional conversion with essentially no further coke formation but with the disadvantage that a certain amount of diolefins are formed. About 25% of the total hydrocarbons from the soaking zone are diolefins. The elimination of these diolefins in the catalytic after treating step substantially improves the stability of the final hydrocarbon products, including both gasoline and middle distillates, so that they are stable as to color and also will not oxidize to form undesirable gums and peroxides. The catalytic after-treating step also improves the octane number of the gasoline fraction of the hydrocarbon products from the present invention, and also eifects a minor amount of additional conversion. Thus, all three major steps, namely, initial catalytic cracking, soaking, and catalytic aftertreating are essential to the present invention so as to produce the overall desirable results of a high ratio of yield of gasoline to yield of coke in addition to stable gasoline and middle distillate products.

As an example of the present process, a catalytic cycle stock containing about 40 weight percent aromatic rings will produce 6% by weight carbon at 40% conversion, 10% by weight at 50% conversion and about 16% by weight at 60% conversion in a conventional catalytic cracking process. From an economic standpoint, it would be very desirable to crack the cycle stock to a conversion of 5055%, for example, except for the high coke yield which would require very large regeneration facilities. Such a requirement is alleviated by the process of the present invention as the cycle stock would be processed to only about 35% conversion in the initial catalytic cracking step of the present invention. The hydrocarbon products from this initial catalytic cracking step would then be maintained at a temperature of about 950 F. for about 1 minute. At the end of this period a total conversion in the order of 50% would be achieved. The coke formation as a result would be only about by weight in the present invention, as compared to 13% by weight in a conventional catalytic cracking process.

In another example where cracking of a high nitrogen content gas oil will produce 6% by weight of coke at 45% conversion and 10% by weight of coke at 55% conversion in a conventional catalytic cracking process, the gas oil would be processed according to the present invention to 35-40% conversion in the initial catalytic cracking step and the resultant hydrocarbon products soaked for about 1 minute at about 950 F. to produce a final conversion of 5055% with a coke yield of less than 5% by weight. In this example, and in the preceding example, the catalytic aftertreating step will produce a minor increase in coke and conversion.

The process of the present invention can be readily understood by reference to the drawing, in which the figure is a diagrammatic view of one form of apparatus adapted to carry out the present invention with parts broken away to facilitate the disclosure.

It is to be understood that the present invention is not limited to the particular apparatus shown in the figure. A reading of the specification will suggested to those skilled in the art other forms of apparatus for carrying out the process of the present invention.

The figure illustrates one form of apparatus for carrying out the process of the present invention when employing a finely divided catalyst which exhibits the properties of a fluid. The catalyst employed may be a silicaalumina, silica-magnesia, etc. catalyst having a particle size range such that substantially all of the catalyst is of a size of about 10-100 microns. It is to be understood, however, that the present process is applicable also to fixed bed and moving bed types of catalytic cracking systems. In the drawing, reference character 10 designates a reaction vessel for carrying out a portion of the process of the present invention, and reference character 11 designates a regenerator for burning oif carbonaceous deposits on the fluidized catalyst in order to restore the catalytic activity of the catalyst. Hydrocarbon gas oil and freshly regenerated catalyst are initially contacted in transfer line reactor 12 in which there is considerable turbulence. The freshly regenerated catalyst at a temperature of about 1000-1300 F. enters one end of reactor 12 by means of standpipe 13 leading from regenerator 11 and the hydrocarbon gas oil enters the same end of reactor 12 by means of conduit 14. Reactor 12, which in this specific embodiment of the present invention is inclined upwards at an angle, provides a contacting zone in which the initial conversion or cracking of the hydrocarbon gas oil to lower boiling components is effected. The temperature in reactor 12 is maintained at about S50-1050 F. and preferably at about 9001000 F. This is accomplished by preheating the hydrocarbon gas oil sufficiently so that when combined with the hot freshly regenerated catalyst leaving regenerator 11, the resultant oil and catalyst mixture is at such a temperature. The rate of flow of freshly regenerated catalyst from regenerator 11 through standpipe 13 is controlled by valve 16 and fluidization of the freshly regenerated catalyst in standpipe 13 is maintained by means of air or steam introduced through line 15. The length and diameter of reactor 12 is sufficient to convert about 30-50% of the hydrocarbon gas oil to gasoline, other low boiling components and coke without producing more than about 5% coke from the hydrocarbon gas oil. The term gasoline refers to hydrocarbon material boiling below 430 F. and includes C s but does not include C s or lighter material. The term other low boiling components includes the C and lighter material. The space velocity of the vaporous hydrocarbon gas oil in reactor 12 is preferably between 10100 w./w./hr. (weight of hydrocarbon feed/weight of catalyst/hr.) and the pressure in reactor 12 is preferably between 15-50 p.s.i.g. In addition, the superficial velocity of the vaporous hydrocarbons in reactor 12 is preferably about 10 to 50 ft./ sec. and the catalyst/ oil ratio on a weight basis is preferably about 5-30.

The partially converted hydrocarbons and partially spent catalyst from reactor 12 are discharged into separating zone 17 of vessel 10. Reactor 12 connects tangentially with vessel 10 so as to impart a centrifugal action on the hydrocarbon vapors and partially spent catalyst. The catalyst particles are thus forced by the centrifugal efiect to the wall of vessel 10 in separating zone 17. Annular plate 18, which defines the upper boundary of separating zone 17, is arranged horizontally on the inside of vessel 10 to aid in the separation of catalyst from the vaporous hydrocarbons. Not more than 20% of the cross-sectional area of vessel 10 is restricted by annular plate 18. The purpose of annular plate 18 is to prevent the layer of catalyst on the wall of vessel 10 from being swept upwardly by the rising hydrocarbon vapors. The superficial velocity of the hydrocarbon vapors is considerably lower in separating zone 17 than in reactor 12, being about 0.5 to 5 ft./sec. In separating zone 17, the partially converted vaporous hydrocarbons are thus separated from the partially spent catalyst, with the partially converted vaporous hydrocarbons flowing upward in vessel 10 through the opening in annular plate 18 and the partially spent catalyst flowing downward along the wall of vessel 10 in separation zone 17 due to the force of gravity. The further processing of these partially converted hydrocarbons will be presently discussed in detail.

The catalyst particles flowing downward from separating zone 17 enter a section of vessel 10 which is smaller in cross-section than separating zone 17 and which operates as stripping zone 19. The catalyst in stripping zone 19 is maintained as a dense turbulent fluidized bed. Steam or other suitable gasv is introduced into the lower portion of stripping zone 19 by means of lines 20, so that substantially all of the hydrocarbons which are entrained with the downflowing catalyst are stripped from the partially spent catalyst. The steam and stripped hydrocarbon vapors from stripping zone 19 rise upward to separating zone 17. Baflles 21 are provided in stripping zone 19 to increase the effectiveness of the stripping operation. The major portion, namely, 50-95%, of the partially spent catalyst from stripping zone 19 flows downward through Standpipe 22 into riser 23. Standpipe 22 is provided with valve 26 which regulates the flow of partially spent catalyst from vessel 10 into riser 23. Standpipe 22 is also provided with line 27 which introduces a fluidizing gas, such as steam, to maintain the partially spent catalyst in a fluid condition.

An oxygen-containing gas is introduced into the bottom end of riser 23 by means of conduit 24 and the mixture of the oxygen-containing gas and partially spent catalyst is passed through riser 23 into the lower part of regenerator 11. Grid 25 is employed at the discharge end of riser 23 to distribute the catalyst-gas mixture uniformly in regenerator 11. A small amount of the coke is burned off the catalyst in riser 23;

In regenerator 11 the remainder of the coke like deposits on the catalyst are burned oil by the oxygencontaining gas. A dense turbulent fluid bed of catalyst particles is maintained in the lower portion of regenerator 11 at a temperature between about 10001300 F. A certain amount of the catalyst is carried upward in regenerator 11 from the dense fluid bed with the flue gases formed during the oxidation reaction. These entrained catalyst particles are removed by cyclone separator 45, or equivalent separating means, arranged at the top of regenerator 11. The flue gases are withdrawn from regenerator 11 by means of conduit 46 and the catalyst particles separated from the tide gas are returned to the dense bed of regenerator 11 by means of dip leg 47.

The partially converted vaporous hydrocarbons after being separated from the partially spent catalyst in separating zone 17 of vessel 10 pass upward through the opening of annular plate 18 into soaking zone 29 in reactor vessel 10. Annular plate 18 in effect defines the boundary between separating zone 17 and soaking zone 29 in vessel 10. A temperature of about 850-1050 F. and preferably about 900-'1000 F. is maintained in soaking zone 29. The average temperature in soaking zone 29 is approximately 15-25 F. lower than the average temperature in reactor 12. This is becas'use the catalytic cracking step in reactor 12 and the thermal cracking step in soaking zone 29 are endothermic reactions which reduce the temperature of the hydrocarbon vapors. It is not necessary to add additional heat to the hydrocarbon vapors in soaking zone 29, although it is within the purview of the present invention to do so. At a temperature preferably of about 9004000 F. the partially converted vaporous hydrocarbons are cracked in soaking zone 29such that an additional 2()% of the hydrocarbons are converted to gasoline and lower boiling components by maintaining the hydrocarbons in soaking zone 29 for about O.5-5 minutes. A minor amount of the thermal cracking also occurs in separating zone 17 after the hydrocarbon vapors are separated from the catalyst and While these vapors are rising to soaking zone 29.

There is essentially no coke formation in soaking zone 29. A very small amount of coke is formed during the thermal cracking step in soaking zone 29 but this amount is insignificant as compared to the coke formed in reactor 12. Also, because a small amount of catalyst may be entrained with the hydrocarbon vapors passing to soaking zone 29 from separating zone 17 a small amount of coke will be formed on this entrained catalyst.

The vaporous hydrocarbon products from soaking zone 29 flow upward into a second contacting zone 30 in vessel 10 wherein the vaporous hydrocarbon products are contacted with partially spent catalyst. A small portion of partially spent catalyst, namely 5-50 of the partially spent catalyst from stripping zone 19, is withdrawn from Standpipe 22 by means of Standpipe 31. Standpipe 31 is provided with valve 32 which regulates the rate of flow of the partially spent catalyst particles in Standpipe 31. Standpipe 31 is also provided with line 33 through which a fluidizing gas, such as stream, is introduced in order to maintain the partially spent catalyst particles in standpipe 31 in a fluid state. The partially spent catalyst particles enter the lower portion of riser 34 from Standpipe 31 Where they are combined with a fluidizing gas, such as steam, which enters the lower portion of riser 34 by means of line 35. The partially spent catalyst particles are carried upwards through riser 34 and are discharged into the upper portion of second contacting zone 30 of vessel 10 above top tray 36. Hroizontally arranged perforated plates or trays 36, 37 and 38 are provided in contacting zone 30 to provide intimate contacting between the hydrocarbon vapors and the partially spent catalyst. The catalyst in zone 30 is maintained in separate dense fluidized beds on plates 36, 37 and 38. The rising hydrocarbon vapors pass through the opening in the plates and then flow through the dense fluidized bed on each plate. Each perforated plate is provided with a downcomer which maintains a definite level of catalyst on each plate and also provides a means for the catalyst to flow from one tray to the tray below. The top of the downcomer of each tray is installed at a suflicient height above the tray so as to maintain the level of the fluidized bed of catalyst on the tray above the bottom of the downcomer from the tray-above in order to prevent the hydrocarbon vapors from passing up through the downcomer to the tray-above. In the drawing, partially spent catalyst discharged from riser 34 forms a dense turbulent fluidized bed on top of plate 36. As additional catalyst is discharged from riser 34 a portion of the catalyst on plate 36 flows into downcomer 39 and passes to plate 37 where it flows to the left in the figure across plate 37. The catalyst then flows into downcomer 40, passes to plate 38, flows across plate 38 to the right in the figure, and passes into downcomer 41. Downcomer 41 differs from the other downcomers in that the catalyst from downcomer 41 is discharged into separating zone 17. Downcomer 41 communicates with separating zone 17 by means or" an opening in annular plate 18. Catalyst leaving downcomer 41 is thus introduced to separating zone 17 at the wall of vessel 10 where the catalyst combines with the catalyst being separated in separating zone 17 and then moves downward due to the force of gravity into the dense fluidized bed in stripping zone 19. The present invention is not restricted to three such plates as shown in the figure since one or more plates can be employed for the purposes of the present invention. Also, any equivalent contacting means could be employed in contacting zone 30. Also, the partially spent catalyst withdrawn from contacting zone 30 could be passed directly to riser 23 or to regenerator 11 after separately stripping any entrained hydrocarbons from it. It is preferable to employ spent catalyst in contacting zone 30 because the purpose of the catalytic aitertreating step in contacting zone 30 is to provide a mild cracking step with little coke formation so as to convert the diolefins which were formed in the thermal cracking step in soaking zone 29 to saturated hydrocarbon forms. This step improves the octane number of the gasoline fraction and, in addition, improves the stability of all the hydrocarbon products from the present invention including the gasoline and middle distillate fractions. Also, a minor amount of additional conversion, namely, 26%, is effected in the catalytic aftertreating step.

The hydrocarbon vapors, or resultant stable lower boilingcomponents from the original hydrocarbon gas oil, rise from contacting zone 30 together with a minor amount of entrained catalyst particles and pass through cyclone separator 42, or equivalent separating means, wherein the vaporous hydrocarbon products are separated from the entrained catalyst. The hydrocarbon vapors essentially free from catalyst leave the top of vessel 10 by means of conduit 43 and the catalyst particles separated from the hydrocarbon vapors in separator 42 are returned to the dense fluid bed on plate 36 in contacting zone 30 by means of dip leg 44.

Other forms of apparatus which will provide the present process will be suggested by studying the figure. For example, it is not necessary that the soaking step and catalytic after-treating step by effected in one vessel, as shown in the present figure, since two separate vessels may be employed to effect the same results. Also, by way of example, it is possible to perform substantially all of the initial catalytic cracking step in the same vessel as is utilized for the thermal cracking and catalytic aftertreating steps, rather than in a separate transfer line reactor as shown in the present drawing. It is therefore Within the spirit of the present invention to employ one vessel or any number of separate vessels for the process of the present invention.

Also, it is possible to employ freshly regenerated catalyst in the catalytic aftertreating step, but as has been previously stated, it is preferable to employ a partially spent catalyst so as to minimize coke formation on the catalyst employed in the catalytic aftertreating step. Although the present invention is especially advantageous for converting gas oils which produce a high proportion of coke to gasoline, such as gas oils having a high aromatic or nitrogen content, the present invention may be advantageously utilized with any type of hydrocarbon cracking feed stock.

The following example of the present process is not intended to limit the present invention but rather to illustrate the operation of the present process and its advantages over conventional catalytic cracking processes. In this example, 1000 liquid barrels/hour of hydrocarbon gas oil are preheated to a temperature of 600 F. and then are introduced into reactor 12. The gas oil has a boiling range of 600-1050 F., and is from a Los Angeles Basin crude oil. At the same time, 1800 tons/hour of synthetic silica-alumina catalyst, having a size range of 10 to 100 microns, at a temperature of 1100 F. are also introduced into reactor 12 from regenerator 11 so that the temperature of the resultant catalyst-oil mixture is 980 F. Under these conditions, the catalyst/oil ratio on a weight basis is approximately 11 to 1 in reactor 12. Reactor 12 is 6 feet in diameter and 50 feet long. The space velocity of the hydrocarbon vapors in reactor 12 is I 40 w./w./hour and the superficial velocity of the hydrocarbon vapors in reactor 12 is 15 ft./sec. The pressure in reactor 12 is p.s.i.g. Under the above cracking conditions, the conversion of the hydrocarbon gas oil to gasoline, other low boiling components and coke is 40% by volume with 5.0% by weight of the hydrocarbon gas oil converted to coke. Approximately 8 tons/hour of coke are thus formed on the catalyst in reactor 12.

The partially converted hydrocarbons and partially spent catalyst from reactor 12 are discharged into separating zone 17 at a temperature of 960 F. and a pressure of 17 p.s.i.g. The superficial velocity of the hydrocarbon vapors in separating zone 17 is 1 ft./scc., and their residence time in separating zone 17 is 10 seconds. The hydrocarbon vapors pass upward from separating zone 17 into soaking zone 29 wherein the average temperature of the hydrocarbon vapors is 950 F. and the pressure 15 p.s.i.g. The residence time of the hydrocarbon vapors in soaking zone 29 is 30 seconds and the superfiicial velocity of the hydrocarbon vapors again is 1 ft./sec. additional 10% by volume of the hydrocarbon vapors is converted to gasoline and other lower boiling components, with about 4.0% of the total hydrocarbon vapors from soaking zone 29 being diolefins.

Approximately 1600 tons/hour of catalyst, on a coke free basis, are withdrawn from standpipe 22 and are combined with 65 M c.f'./minute of air in riser 23. In the regeneration step, 10.5 ton/hour of coke are burned off the catalyst in riser 23 and regenerator 11 at a temperature of 1100 F.

At the same time, 200 tons/hour of catalyst, on a coke free basis, are withdrawn from standpipe 22 by means of standpipe 31 and are combined in riser 34 with 7000 lbs/hour of steam from conduit 35. The 200 tons/ hour of partially spent catalyst are discharged from riser 34 onto top plate 36 of a series of plates 36, 37 and 38 of contacting zone 30 on each of which plates a fluid bed of catalyst 8 inches in height is maintained. The temperature in contacting zone 30 is 950 F. and the pressure in the zone is 14 p.s.i.g. Approximately 2.5 tons/hour of coke are formed on the catalyst in contacting zone 30, and an additional conversion of 4% is efiected in this zone. From contacting zone 30, about 200 tons/hour of catalyst on a coke free basis are withdrawn by means of downcomer 41 and are passed to separating zone 17. Hydrocarbon products are withdrawn from the upper part of vessel 10 through conduit 43 and less than 1.0% of the total hydrocarbon products are undesirable diolefins. The gasoline fraction of the final hydrocarbon products has an octane number (F-l) of and the total conversion effected in this example of the present invention is 54%.

In a conventional catalytic cracking process to obtain the same percentage conversion with the particular type of gas oil and type of catalyst employed in the above example, and when employing the same hydrocarbon gas oil feed rate as above, 16.5 tons/hour of coke would be formed on the catalyst. The gasoline fraction from the conventional catalytic cracking process would have an octane number (F-l) of 95, being therefore no higher than in the process of the present invention, and the diolefin content of the total hydrocarbon products would be 1.0%.

Thus, the overall liquid product quality and yields from a conventional catalytic cracking process and the process of the present invention are equivalent for all practical purposes in this comparison. However, a conventional catalytic cracking process will produce 55% more coke for the same percentage of conversion and would therefore require 55% more regeneration capacity to burn the coke off of the catalyst. Another way of looking at the advantages of the present process is that, in a conventional catalytic cracking system, if catalyst regeneration facilities are limited to burning 10.5 tons of coke/hour, the conversion of hydrocarbons to gasoline, other low boiling components and coke will be limited to about 44% conversion in the conventional catalytic cracking system as compared to 54% conversion in the present process.

What is claimed is:

1. A process for the conversion of hydrocarbons to stable lower boiling components which comprises contacting gas oil hydrocarbons with freshly regenerated catalyst in a contacting zone at a temperature of about 850- 1050 F., maintaining said hydrocarbons in contact with said catalyst in said contacting zone at said temperature to thereby produce partially converted vaporous hydrocarbons and partially spent catalyst until about 30-50% by volume of said hydrocarbons is converted to coke and components boiling below about 430 F. but not more than about 5% by weight of said hydrocarbons is converted to coke, passing the total eflluent from said contacting zone to a separating zone and separating substantially all of said partially converted vaporous hydrocarbons from said partially spent catalyst, passing said separated partially converted vaporous hydrocarbons substantially free of said partially spent catalyst from said separating zone as the only stream into a soaking zone, maintaining s'aid partially converted vaporous hydrocarbons in said soaking zone, at a lower average temperature than in said contacting zone and between a temperature of 850-1050" F. for about 0.5- minutes to thereby further convert said partially converted vaporous hydrocarbons so that an additional 5-20% by volume of said vaporous hydrocarbons is converted to components boiling below about 430 E, and a small amount of coke, contacting the total effluent of converted" vaporous hydrocarbons from said soaking zone with a portion of said separated partially spent catalyst in a second contacting zone to thereby produce said stable lower boiling hydrocarbon components and middle distillate oil fractions, separating said stable lower boiling components from said partially spent catalyst from said second contacting zone, and regenerating said partially spent catalyst from both of said contacting zones in a regeneration zone.

2. In the conversion of a hydrocarbon gas oil to stable lower boiling components, the improvement which comprises contacting said hydrocarbon gas oil with freshly regenerated catalyst at a temperature of at least about 900 F. until about 30-50% by volume of said hydrocarbon gas oil is conyerted'to coke and components boiling below about 430 F. and such that not more than about 5% by weight of said hydrocarbon gasoil is converted to coke, separating the total resultant partially converted vaporous hydrocarbons from the resultant partially spent catalyst on which said coke is deposited, holding said separated partially converted hydrocarbons at a temperature of at least 900 F. and at a lower temperature than in the first contacting step until at least about 5% by volume more of said hydrocarbons is converted to components boiling below about 430 F. and a small amount of coke, then contacting the total resultant further converted vaporous hydrocarbons with a portion of said separated partially spent catalyst to form said stable lower boiling components and middle distillate oil fractions, separating said stable lower boiling components and middle distillate oil fractions from said portion of said partially spent catalyst, and regenerating said partially spent catalyst.

3, A process for the conversion of hydrocarbons to stable lower boiling components and middle distillate oil fractions which comprises contacting gas oil hydrocarbons with hot freshly regenerated catalyst to produce vaporous hydrocarbon reaction products, separating the total resultant vaporous hydrocarbon reaction products from the partially spent catalyst, passing said total separated vaporous hydrocarbon reaction products through a soaking zone to effect further conversion, contacting the total resultant vaporous hydrocarbon reaction products from said soaking zone with a portion of said separated partially spent catalyst to produce said stable lower boiling components and middle distillate oil fractions, separating said stable lower boiling components and middle distillate oil fractions fromsaid partially spent catalyst, and regenerating said partially spent catalyst to produce said freshly regenerated catalyst.

4. A process for the conversion of hydrocarbons to lower boiling components which comprises mixing gas oil hydrocarbons with freshly regenerated catalyst in a contacting zone at a temperature of about 900-1 000 F., maintaining said hydrocarbons in said contacting zone until about 30-50% by volume of said hydrocarbons is converted to coke and components boiling below about 430 F. but not more than 5% by weight of said hydrocarbons is converted to coke which is deposited on said catalyst, separating the total resultant vaporous hydrocarbons from said partially spent catalyst, passing said total resultant vaporous hydrocarbons from said contacting zone as the only stream into a soaking zone and maintaining said hydrocarbons in said soaking zone at a temperature of about 900-1000 F. but not higher than in said first contacting zone until an additional 540% by volume of said hydrocarbons is converted to components boiling below about 430 F., and a small amount of coke, withdrawing substantially all of the vaporous hydrocarbons from said soaking zone and contacting said withdrawn vaporous hydrocarbons with a portion of said partially spent catalyst in a second contacting zone, separately withdrawing substantially all of the vaporous hydrocarbons and said partially spent catalyst from said second contacting zone, and regenerating said partially spent catalyst from both of said contacting zones in a regeneration zone.

5. A process for converting hydrocarbons to stable lower boiling components and middle distillate oil fractions which comprises mixing gas oil hydrocarbons with hot freshly regenerated catalyst in a transfer line reaction zone, maintaining said hydrocarbons and said catalyst in said reaction zone at a temperature of about 900-1000 F. until about 30-50% by volume of said hydrocarbons is converted to coke and components boiling below about 430 F. but notmore than about 5% by weight of said hydrocarbons is converted to coke which is deposited on said freshly regenerated catalyst to produce partially spent catalyst, withdrawing substantially all of the resultantpartially converted vaporous hydrocarbons and said partially spentcatalyst from said reaction zone, passing said withdrawn partially converted vaporous hydrocarbons and said partially spent catalyst into a separating zone, separating substantially all of the said partially converted vaporous hydrocarbons from said partially spent catalyst, separately withdrawing substantially all of said partially converted vaporous hydrocarbons and said partially spent catalyst from said separating zone as separate streams, passing substantially all of said partially converted vaporous hydrocarbons substantially free from said partially spent catalyst and as the only stream into a soaking zone, maintaining said hydrocarbons in said soaking zone at a temperature of about 900-l000 F. but not higher than in said transfer line reactor until an additional 5-20% by volume of said hydrocarbons is converted to components boiling below about 430 F., and a small amount of coke, withdrawing substantially all of the resultant further converted vaporous hydrocarbons from said soaking zone and passing them into a contacting zone, contacting said further converted vaporous hydrocarbons in said contacting zone with a minor portion of said separated partially spent catalyst from said separating zone to produce said stable lower boiling components and middle distillate oil fractions, separating said stable lower boiling components and middle distillate oil fractions from said contacting zone from said partially spent catalyst, passing said partially spent catalyst from said contacting zone into said separating zone, and regenerating the major portion of said partially spent catalyst from said separating zone in a regeneration zone to thereby produce said hot freshly regenerated catalyst.

6. A process for converting hydrocarbons to stable lower boiling components and middle distillate oil fractions which comprises mixing gas oil hydrocarbons with hot freshly regenerated catalyst in a transfer line reaction zone, maintaining said hydrocarbons and said catalyst in said reaction zone at a temperature of about 900-1000 F. until about 30-50% by volume of said hydrocarbons is converted to coke and components boiling below about 430 F. but not more than about 5% by weight of said hydrocarbons is converted to coke which is deposited on Said freshly regenerated catalyst to thereby produce partially spent catalyst, separating from each other in a separating zone substantially all of the resultant partially converted vaporous hydrocarbons and said partially spent catalyst from said reaction zone, passing the separated partially spent catalyst to a stripping zone in order to remove absorbed partially converted vaporous hydrocarbons from said separating partially spent catalyst, passing substantially all of the partially converted vaporous hydrocarbons from said separating and stripping zones as the only stream into a soaking zone and maintaining said partially converted vaporous hydrocarbons in said soaking zone at a temperature of about 900-1000 F. but at a lower temperature than in said transfer line reaction zone until an additional -20% by volume of said hydrocarbons is converted to components boiling below about 430 F., and a small amount of coke, passing substantially all of the resultant further converted vaporous hydrocarbons from said soaking zone into a contacting zone, withdrawing a minor portion of said partially spent stripped catalyst from said stripping zone, passing said withdrawn minor portion of said partially spent stripped catalyst into said contacting zone, contacting substantially all of the further converted vaporous hydrocarbons with said minor portion of said partially spent stripped catalyst in said contacting zone in order to produce stable middle distillate oil fractions and to convert substantially all diolefins in said further converted vaporous hydrocarbons to saturated hydrocarbons to thereby produce said stable lower boiling components, separately withdrawing from said contacting zone said lower boiling components and said middle distillate oil fractions and the resultant further partially spent catalyst, passing the separated further partially spent catalyst to said stripping zone to remove absorbed hydrocarbons from said further partially spent catalyst, withdrawing the major portion of said partially spent catalyst including said further partially spent catalyst from said stripping zone, and passing said major portion of said partially spent catalyst from said stripping zone into a regeneration zone to thereby produce said hot freshly regenerated catalyst.

7. A process for the cracking of higher boiling hydrocarbons to produce lower boiling hydrocarbons in the gasoline boiling range which comprises contacting hydrocarbon gas oil with a cracking catalyst under cracking conditions to produce vaporous cracked hydrocarbons, then passing said total cracked vaporous hydrocarbons as the only stream to a soaking zone maintained at a temperature to effect further conversion of the vaporous cracked hydrocarbons while producing only a small amount of coke, removing the total cracked vaporous hydrocarbons from said soaking zone and then contacting the removed total cracked vaporous hydrocarbons with partially spent cracking catalyst from said first contacting step to convert unsaturated hydrocarbons to stable hydrocarbons.

8. A process according to claim 7 wherein the cracked vaporous hydrocarbons contain gasoline hydrocarbons and middle distillate oil fractions which form stable hydrocarbons during the second contacting step with partially spent cracking catalyst.

References Cited in the file of this patent UNITED STATES PATENTS 2,303,944 Mangelsdorf Dec. 1, 1942 2,327,099 Eastman Aug. 17, 1944 2,378,531 Becker June 19, 1945 2,430,096 Barcus Nov. 4, 1947 2,436,486 Scheineman Feb. 24, 1948 2,444,131 Delattre-Seguy June 29, 1948 2,681,304 Blanding et a1. June 15, 1954 2,737,474 Kimberlin et al- Mar. 6, 1956 

3. A PROCESS FOR THE CONVERSION OF HYDROCARBONS TO STABLE LOWER BOILING COMPONENTS AND MIDDLE DISTILLATE OIL FRACTIONS WHICH COMPRISES CONTACTING GAS OIL HYDROCARBONS WITH HOT FRESHLY REGENERATED CATALYST TO PRODUCE VAPOROUS HYDROCARBON REACTION PRODUCTS, SEPARATING THE TOTAL RESULTANT VAPOROUS HYDROCARBON REACTION PRODUCTS FROM THE PARTIALLY SPENT CATALYST PASSING SAID TOTAL SEPARATED VAPOROUS HYDROCARBON REACTION PRODUCTS THROUGH A SOAKING ZONE TO EFFECT FURTHER CONVERSION, CONTACTING THE TOTAL RESULTANT VAPOROUS HYDROCARBON REACTION PRODUCTS FROM SAID SOAKING ZONE WITH A PORTION OF SAID SEPARATED PARTIALLY SPENT CATALYST TO PRODUCE SAID STABLE LOWER BOILING COMPONENTS AND MIDDLE DISTILLATE OIL FRACTIONS, SEPARATING SAID STABLE LOWER BOILING COMPONENTS AND MIDDLE DISTILLATE OIL FRACTIONS FROM SAID PARTIALLY SPENT CATALYST, AND REGENERATING SAID PARTIALLY SPENT CATALYSTTO PRODUCE SAID FRESHLY REGENERATED CATALYST. 